Light-emitting devices with improved active-region

ABSTRACT

A light-emitting device comprises an active-region sandwiched between an n-type layer and a p-type layer, that allows lateral carrier injection into the active-region so as to reduce heat generation in the active-region and to minimize additional forward voltage increase associated with bandgap discontinuity. In some embodiments, the active-region is a vertically displaced multiple-quantum-well (MQW) active-region. A method for fabricating the same is also provided.

1. FIELD OF THE INVENTION

The present invention relates in general to light-emitting devices, moreparticularly to light-emitting devices with enhanced carrier injection,reduced heat generation and light absorption.

2. DESCRIPTION OF THE RELATED ART

Besides the electron supplier layer (n-type layer) and hole supplierlayer (p-type layer), the most important layer in a light-emittingdevice is the active-region sandwiched between the n-type layer and thep-type layer. Non-equilibrium electrons and holes are injected into theactive-region to radiatively recombine, resulting in light-emitting. Theinjected carriers (electrons and holes) will experience attractive forcefrom carriers with opposite charge type, and repulsive force fromcarriers with identical charge type. It is the attractive force thathelps to form electron-hole pairs and increase electron-hole (e-h)recombination probability. For this reason, it is highly desirable toconfine the injected carriers in a limited area/volume to have betterlight-emitting efficiency. In the past decades, active-region has beendeveloped from three-dimensional (3D), to two-dimensional (2D), even toone- and zero-dimensional (1D, 0D). A 3D active-region is made of aquasi bulk material without any quantum confinement effect, wherecarriers can diffuse three-dimensionally and the e-h recombinationprobability is low. A 2D active-region has quantum confinement usuallyin the direction of carrier injection, commonly of multiple-quantum-well(MQW) configuration. 1D and 0D active-regions implement additionalquantum confinement in other directions, with quantum wire and quantumdot as representatives.

Compared to 3D active-region, 2D MQW active-region has much higher e-hrecombination probability yet without adding fabrication complexity. MQWthus is the most commonly adopted active-region for modernlight-emitting devices.

An MQW consists of many alternating quantum barriers (also referred toas barrier throughout this specification) and quantum wells (alsoreferred to as well throughout this specification), with quantumbarriers having larger bandgap energy. When sandwiching quantum wells,these barriers provide quantum confinement to carriers injected intoquantum wells, leading to a superior radiative recombination rate. Theband structure of an exemplary GaN/InGaN MQW LED is given in FIG. 1. Asshown, the GaN barriers and InGaN wells have band discontinuities inconduction band as well as in valence band. Usually, the banddiscontinuity in conduction band is more pronounced, forming potentialbarriers for the electrons in the wells. The valence band discontinuityprovides potential barriers to confine holes in the quantum wells. Thus,injected non-equilibrium electrons and holes are confined in the quantumwells, in the direction perpendicular to the quantum well layer, whichcoincides with the carrier injection direction in the prior artlight-emitting device. This confinement greatly increases theelectron-hole oscillation strength, leading to enhanced e-hrecombination probability.

However, the inventors point out that there are certain drawbacks in theprior art practice using MQW as active region. Referring to FIG. 1(holes illustrated by hollow circles), when carriers are driven fromquantum barriers into quantum wells, there is a potential energy loss ofthe carriers. This potential energy will be converted first intocarriers' kinetic energy, then totally into heat as carriers relax theirkinetic energy via phonons emission. The heat generation for electronsinjection is severer since conduction band discontinuity is larger thanvalence band discontinuity.

For example, in commercial blue/green LEDs, GaN and InGaN are used asquantum barrier and quantum well materials in the MQW, respectively.There is a bandgap discontinuity of 0.5-0.8 eV between the quantumbarriers and quantum wells. When these commercial LEDs are driven under1 A current for general lighting applications, according to theinventors' finding, there is 0.5-0.8 watt heat generated in the MQWactive-region, because of the perpendicular carrier injection to the MQWand the bandgap discontinuity in that direction. This heat associatedwith MQW bandgap discontinuity, being generated right inside thelight-emitting region, is expected to be very deleterious to theelectric-optical power conversion efficiency. Especially in the highcurrent injection regime, this heat generation could be the root for thecommonly observed efficiency droop (efficiency droop is explained in USpatent application publication No. 2009/0050924, the contents of whichis hereby incorporated by reference in its entirety).

Another disadvantage of the prior art MQW structure is that carriers arerepeatedly pumped up into barriers from wells in order to reach thefurthest quantum wells. Referring to FIG. 1, electrons first injectedinto QW1 (first quantum well) have to be pumped up into additionalbarriers in order to reach QW2 (second quantum well) and QW3 (thirdquantum well). This increases device resistance and, thus, increasesdevice forward voltage. Ni et al (Reduction of efficiency droop in InGaNlight emitting diodes by coupled quantum wells, Appl. Phys. Lett. 93,171113 (2008)) has reported to use thin quantum barriers in order tofacilitate carriers' tunneling transport. However, tunneling barriersinevitably has less quantum confinement effect, leading to a reducedradiative recombination rate.

U.S. Pat. No. 7,611,917, the contents of which is hereby incorporated byreference in its entirety, describes a method to generate growth pits inthe epilayer and expects the light-emitting active-region can extendinto the pits area, enabling improved hole injection. Similarly, USpatent application publication No. 2009/0191658, the contents of whichis hereby incorporated by reference in its entirety, also proposesgrowth pits for enhanced hole injection. Further, US 2009/0191658suggests ion implantation or diffusion as a post-growth approach to formp-type region penetrating active-region. It also mentions selectiveetching of active-region and performing p-type layer regrowth to fill upthe etched active-region. All these approaches in general can result inbetter hole injection. While the pits formation approach sacrifices thedevice structure quality, the other post-growth approaches will damagethe active-region. This means that the approaches proposed by U.S. Pat.No. 7,611,917 and US patent application publication No. 2009/0191658will lead to degraded device performance such as large device leakagecurrent, poor reverse sustaining voltage and low electrostatic dischargeperformance.

In brief, modern light-emitting devices utilizing heterostrucutresgreatly improves light-generation efficiency. However, the bandgapdiscontinuity associated with heterostrucutre will inevitably set upbarriers for carrier's injection in the direction perpendicular to theheterostrucutre interfaces (heterointerfaces). This hindrance tocarrier's injection will become much severer for wide bandgapsemiconductors where carriers have large effective mass. Also, whenbeing injected from a wide bandgap layer to a narrow bandgap layer,carriers lose the potential energy by emitting phonons. Thiscarrier-lattice interaction process produces heat which will reducelight-emitting device's efficiency, especially when the device is drivenunder high current-injection regime for general lighting applications.

3. SUMMARY OF THE INVENTION

The present invention discloses new carrier injection schemes to reduceor avoid heat generation in MQW and to minimize or eliminate additionalforward voltage increase associated with bandgap discontinuity.

One aspect of the present invention provides a light-emitting devicethat comprises an n-type layer, a p-type layer, and an active-region,wherein the n-type layer is in contact with the active-region in a firstcontact area substantially perpendicular to the active-region forlaterally injecting electrons into the active-region.

Preferably, the p-type layer is also in contact with the active-regionin a second contact area substantially perpendicular to theactive-region for laterally injecting holes into the active-region.Preferably, the active-region is made of multiple barrier layers andwell layers. In some embodiments, the active-region contains 20-50 pairsof the well layers and the barrier layers.

In some embodiments, the total thickness of the active-region is in therange from 400 nm to 1000 nm. The thickness of each of the barrierlayers is in the range from 10 nm to 300 nm. In some embodiments, atleast two of the well layers emit different wavelength emissions with apeak wavelength difference at least 10 nm.

The substrate for accommodating the n-type layer, the p-type layer, andthe active-region can be selected from the group consisting of GaN,sapphire, silicon, silicon carbide, zinc oxide, quartz, glass andgallium arsenide.

Another aspect of the present invention provides a light-emitting devicethat comprises an n-type layer, a p-type layer, and a verticallydisplaced active-region sandwiched between the n-type layer and thep-type layer.

The active-region contains a plurality of volume units, each beingdefined by a top surface, a bottom surface and a sidewall; adjacentvolume units are vertically displaced so that the top surfaces of theadjacent volume units are not in a plane, or the bottom surfaces of theadjacent volume units are not in a plane; the sidewalls of the volumeunits are divided into two groups, a first group of sidewalls areexposed to the n-type layer for receiving electrons laterally injectedfrom the n-type layer, a second group of sidewalls are exposed to thep-type layer for receiving holes laterally injected from the p-typelayer. Each of the sidewalls exposes more than one well layer.

In some embodiments, the top surfaces of the volume units substantiallylie in two vertically separated planes, respectively, or in more thantwo vertically separated planes, respectively.

In some embodiments, all of the volume units have the same number ofwell layers and substantially the same height, and adjacent volume unitsshare a vertically overlapping portion that contains at least one welllayer.

In some embodiments, the ratio of a contact surface area between then-type layer and a first group of sidewalls of the volume units to acontact surface area between the p-type layer and a second group ofsidewalls of the volume units is in the range of 0.5 to 2.

Another aspect of the present invention provides a light-emitting devicethat comprises an n-type layer, a p-type layer, and a light-emittingactive-region sandwiched between the n-type layer and the p-type layer,wherein the active-region has a plurality of first projectionsprotruding towards the n-type layer, sidewalls of the first projectionsare exposed to the n-type layer and able to receive electrons laterallyinjected from the n-type layer.

In some embodiments, the active-region further has a plurality of secondprojections protruding towards the p-type layer, sidewalls of the secondprojections are exposed to the p-type layer and able to receive holeslaterally injected from the p-type layer.

Preferably, the active-region comprises multiple well layers and barrierlayers, the sidewalls of the first projections expose more than one welllayer.

In some embodiments, the first projections comprise projections that areseparated from each other. In some other embodiments, the firstprojections comprise projections that are connected with each other toform a continuous structure.

Another aspect of the present invention provides a light-emitting devicethat comprises an n-type layer with a plurality of first projections, ap-type layer, and a light-emitting active-region with multiple welllayers and barrier layers sandwiched between the n-type layer and thep-type layer. The active-region has a plurality of first recessescorresponding to the first projections of the n-type layer, each of thefirst recesses accommodates one of the first projections, and sidewallsof the first recesses expose more than one well layer and are able toreceive electrons laterally injected from the first projections of then-type layer.

In some embodiments, the active-region also has a plurality of secondrecesses, the p-type layer has a plurality of second projections, eachof the second recesses accommodates one of the second projections, andsidewalls of the second recesses expose more than one well layer and areable to receive holes laterally injected from the second projections ofthe p-type layer.

In some embodiment, the first recesses penetrate the entireactive-region and are partially filled with a p-type material and aninsulating material which separates the p-type material from the firstprojections, and the p-type material is connected to the p-type layer.

In some embodiments, the first projections comprise projections that areseparated from each other. In some embodiments, the first projectionscomprise projections that are connected with each other to form acontinuous structure.

In some embodiments, the second recesses penetrate the entireactive-region and are partially filled with an insulating material so asto separate the second projections from the n-type layer. In someembodiments, the first recesses penetrate the entire active-region andare partially filled with another insulating material so as to separatethe first projections from the p-type layer.

Another aspect of the present invention provides a method formanufacturing a light-emitting device. The method comprises providing ann-type layer deposited over a substrate; patterning the n-type layer toform a plurality of recesses defining a first group of surfaces and asecond group of surfaces vertically displaced from the first group ofsurfaces; depositing an active-region over and conformable to thesurface of the n-type layer, so that a first portion of theactive-region is formed on the first group of surfaces and a secondportion of the active-region is formed on the second group of surfaces,wherein the first portion of the active-region is vertically displacedfrom the second portion of the active-region; and depositing a p-typelayer over and conformable to the active-region,

Preferably, the step of depositing the active-region includesalternately depositing multiple well layers and barrier layers.Sidewalls of the first portion of the active-region that are in contactwith the n-type layer expose at least one well layer and sidewalls ofthe second portion of the active-region that are in contact with thep-type layer expose at least one well layer.

In some embodiments, the method includes, before depositing theactive-region, further depositing a recovery n-type layer on the n-typelayer, which covers the first group of surfaces and the second group ofsurfaces of the n-type layer.

In some embodiments, the method includes, before depositing theactive-region, further depositing an insulating layer on the n-typelayer, which covers the first group of surfaces and the second group ofsurfaces of the n-type layer, but does not cover sidewalls connectingthe first group of surfaces and the second group of surfaces.

Another aspect of the present invention provides a method formanufacturing a light-emitting device. The method comprises:

providing an n-type layer deposited over a substrate; forming aninsulating layer on the n-type layer;

patterning the insulating layer to remove exposed portion of theinsulating layer and a portion of the n-type layer below the exposedportion of the insulating layer, resulting in a first group of surfacesof a remaining insulation layer and a second group of surfaces of aremaining n-type layer vertically displaced with the first group ofsurfaces;

depositing an active-region, so that a first portion of theactive-region is formed on the first group of surfaces and a secondportion of the active-region is formed on the second group of surfaces;

removing the first portion of the active-region to expose the remaininginsulating layer;

depositing a p-type layer over the active-region to cover top surface ofthe active-region, wherein a portion of the p-type layer fills the spacethat was occupied by the removed first portion of the active-region toform a plurality of hole injection plugs;

patterning and etching the p-type layer to remove some of the holeinjection plugs and the remaining insulating layer therebeneath untilthe n-type layer is expose so as to form a plurality of electroninjection plug holes; and

depositing another n-type layer into the plurality of electron injectionholes to form a plurality of electron injection plugs; and

depositing another insulating layer on the plurality of electroninjection plugs to insulate the plurality of electron injection plugsfrom the p-type layer.

Preferably, the step of depositing the active-region includesalternately depositing multiple well layers and barrier layers. The holeinjection plugs are in contact with at least one well layer, and theelectron injection plugs are in contact with at least one well layer.

In some embodiments, the method includes, before depositing theactive-region, further depositing a recovery n-type layer on the n-typelayer, which covers the first group of surfaces and the second group ofsurfaces.

Another aspect of the present invention provides a method formanufacturing a light-emitting device. The method comprises:

providing a p-type layer, an insulating layer, and an n-type layerdeposited over a substrate;

patterning and etching the p-type layer and the insulating layer untilthe n-type layer is exposed, so as to form a plurality of projectionscontaining a remaining portion of the p-type layer and a remainingportion of the insulating layer;

depositing an active-region with multiple well layers and barrier layersover the substrate so that the projections penetrate the active-regionand expose the remaining portion of the p-type layer to more than onewell layers.

In some embodiments, the step of patterning and etching the p-type layerand the insulating layer etches into the n-type layer for apredetermined thickness.

4. BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and constitute a part of thisapplication, illustrate embodiments of the invention and together withthe description serve to explain the principle of the invention. Likereference numbers in the figures refer to like elements throughout, anda layer can refer to a group of layers associated with the samefunction.

FIG. 1 shows the calculated band structure of a GaN/InGaN MQW LED underzero bias.

FIG. 2A-FIG. 2D illustrate the structure and fabrication process flow ofan embodiment according to the present invention.

FIG. 3A-FIG. 3C illustrate the structure and fabrication process flow ofan embodiment according to the present invention.

FIG. 4A-FIG. 4E illustrate the structure and fabrication process flow ofan embodiment according to the present invention.

FIG. 5A-FIG. 5J illustrate the structure and fabrication process flow ofan embodiment according to the present invention.

FIG. 6 shows an example of two-dimensional etch pattern, a square grid.

FIG. 7 shows an example of two-dimensional etch pattern, a squarelattice of circles.

FIG. 8 shows an example of two-dimensional etch pattern, a chessboard.

5. DETAILED DESCRIPTION OF EMBODIMENTS

The principle of the present invention can be applied to light-emittingdevices such as LEDs, laser diodes, and can also be applied to photodetector diodes by those who are skilled in the art based on theteachings in this specification. For convenience and simplicity, theinventors use GaN-based LEDs as an example to describe the embodimentsof the present inventions. It should be understood that the presentinvention is by no means limited to GaN-based LEDs.

According to one aspect of the present invention, a light-emittingdevice, or a light emitting diode (LED) capable of injecting holes indirection parallel to MQW layers, or capable of lateral injection ofholes into MQW is provided. The structure and fabrication process ofsuch light-emitting device are disclosed. The fabrication processincludes these steps:

to provide a template, which includes a thick n-type semiconductor layerdeposited over a substrate, an insulating semiconductor layer depositedover the n-type layer, and a p-type semiconductor layer deposited on theinsulating layer;

to shape the template, which includes to form masks on the template, toperform etching to access the n-type layer through the unmasked areasand form two groups of vertically displaced surfaces, and to remove themasks;

to resume LED growth on the shaped template, which includes to deposit athin n-type layer to recover the surfaces, to deposit MQW active-regionover the recovered surfaces, and to deposit p-type layers over the MQWactive-region.

According to another aspect of the present invention, an LED capable oflateral injection of holes and electrons is provided. The fabricationprocess includes:

to provide a template which includes a thick n-type semiconductor layerdeposited over a substrate;

to shape the template, which includes to form masks on the template, toperform etching to form two groups of vertically displaced surfaces, andto remove the masks;

to resume LED growth on the shaped template, which includes to deposit athin n-type layer to recover the surfaces, to deposit MQW active-regionover the recovered surfaces, and to deposit p-type layers over the MQWactive-region.

According to still another aspect of the present invention, an LEDcapable of lateral injection of electrons is provided. The fabricationprocess includes:

to provide a template which includes a thick n-type semiconductor layerdeposited over a substrate, an insulating semiconductor layer depositedover the n-type layer;

to shape the template, which includes to form masks on the template, toperform etching to access the n-type layer through the unmasked areasand form two groups of vertically displaced surfaces, and to remove themasks;

to resume LED growth on the shaped template, which includes to deposit athin n-type or insulating layer to recover the surfaces, to deposit MQWactive-region over the recovered surfaces, and to deposit p-type layersover the MQW active-region.

According to still another aspect of the present invention, an LEDenabling simultaneous lateral injection of electrons and holes into thesame MQW active-region is provided. The fabrication process includes:

to provide a template which includes a thick n-type semiconductor layerdeposited over a substrate, an insulating semiconductor layer depositedover the n-type layer;

to shape the template, which includes to form masks on the template, toperform etching to access the n-type layer through the unmasked areasand form two groups of vertically displaced surfaces, and to remove themasks;

to resume epitaxial growth on the shaped template, which includes todeposit a thin n-type or insulating layer to recover the surfaces, todeposit MQW active-region over the recovered surfaces;

to form masks a second time, covering/protecting the recessed MQW areas;

to perform etch a second time, to remove the unmasked MQW areas;

to remove the second masks, and resume p-layers growth;

to form masks a third time, and perform etch to access the n-type layer;

to resume epitaxial growth of an n-type layer and an insulating layer,with the n-type layer grown first in contact with the bottom n-typelayer over substrate.

FIG. 2A-FIG. 2D illustrate the structure and fabrication process of anLED embodiment of the present invention enabling lateral hole injectioninto MQW active-region. Referring to FIG. 2A, an n-type layer 20 isdeposited over a substrate 10. The n-type layer 20 can be made of thesame material as that of the substrate 10, or can be made of differentmaterial, i.e., n-type layer 20 can be grown homoepitaxially orheteroepitaxially on substrate 10. In the case of heteroepitaxialgrowth, there may be other layers formed between n-type layer 20 andsubstrate 10, such as a buffer layer to accommodate lattice mismatchbetween n-type layer 20 and substrate 10. In the case of GaN-based LEDs,n-type layer 20 can be Si-doped GaN, Si-doped AlGaN, or Si-doped InGaNlayer. Substrate 10 can be made of GaN, sapphire, silicon, siliconcarbide, quartz, zinc oxide, glass and gallium arsenide, and the likeused in the field of interest. On top of n-type layer 20 is formed aninsulating layer 30, which is followed by a p-type layer 40. Theinsulating layer 30 can be insulating GaN such as intrinsic GaN, irondoped GaN, or highly compensated doped GaN layer, or insulating AlGaN orAlN layer. Insulating layer 30 is used for electrical isolation so itsresistivity is preferred to be high, preferably to be higher than 100Ω·cm, more preferably to be higher than 1000 Ω·cm. P-type layer 40 canbe p-type nitride such as magnesium doped GaN, InGaN, or AlGaN layer.

Referring to FIG. 2A and FIG. 2B, a mask 15 is used to define etchpatterns. The etch depth should be equal to or greater than the sum ofthickness d₃ of insulating layer 30 and thickness d₄ of p-type layer 40,to expose n-type layer 20 and allow full electrical access to n-typelayer 20 by an active-region formed later. Thickness, d₃, of insulatinglayer 30 is preferably in the range of 0.1 μm-0.5 μm, and thickness, d₄,of p-type layer 40 is preferably in the range of 0.2 μm-0.6 μm, but d₃and d₄ are not limited to these thickness ranges.

After etching, mask 15 is removed to expose top surface 401 of remainingp-type layer 40′ and top surface 201 of a portion of n-type layer 20.The two groups of surfaces 401 and 201 are vertically displaced as shownin FIG. 2B, for the following LED structure growth, which starts withthe deposition of an optional recovery n-type layer 22 torecover/refresh the etched surfaces of n-type layer 20 for next MQWactive-region growth. The recovery n-type layer 22 can be GaN, InGaN, orAlGaN layer, with thickness from 0.1 to a few microns, for example 3 μm.Preferably, the recovery layer thickness is in the range of 0.1-0.5microns. Referring to FIG. 2C, recovery n-type layer 22 includes twoportions: layers 221 and 222 recovering surfaces 201 and 401,respectively. The thickness of layer 221 should be less than the sum ofthe thickness of remaining insulating layer 30′ and the thickness etchedinto n-type layer 20, so that layer 221 is not in direct contact withremaining p-type layer 40′. An MQW active-region 50 (includingactive-region 501 formed on layer 221 and active-region 502 formed onlayer 222) is then deposited layer-by-layer over recovery n-type layers221 and 222. The MQW active-region 50 is in general made of alternateAlInGaN quantum barriers and AlInGaN quantum wells, with GaN or InGaNbarriers and InGaN wells as a special case. Finally, over the MQWactive-region 50 a thick p-type layer 60 is grown to finish thestructure. Depending on the etch depth and the regrowth thickness, layer60 can have a flat surface (FIG. 2C) or an uneven surface (FIG. 2D).When the surface of layer 60 is uneven, other materials with differentrefractive index can be filled to smooth the uneven surface. As shown inFIG. 2D, uneven surface of layer 60 is smoothened out by fillingmaterial 70. Material 70 can be dielectrics like silicon dioxide,silicon nitride, or be transparent conducting oxides like ITO.

With the structure shown in FIGS. 2C and 2D, lateral hole injection intoMQW active-region 501 is realized. In FIG. 2C and FIG. 2D, hole currentand electron current are represented by hollow and solid arrows,respectively. As seen, besides the conventional perpendicular holeinjection, there is substantial lateral hole injection into MQWactive-region 501 via sidewalls of remaining p-type layer 40′. Since MQWactive-region 501 strides over sidewalls of remaining insulating layer30′ and sidewalls of remaining p-type layer 40′, hole lateral injectioninto sidewalls of MQW active-region 501 is implemented while leakagepath being eliminated from remaining p-type layer 40′ to recovery n-typelayer 221.

Optionally, MQW active-region 502 and/or recovery n-type layer 222 canbe removed before depositing p-type layer 60. Optionally, other layersuch as a p-type layer with larger bandgap energy than p-type layer 60can be formed between p-type layer 60 and MQW active-region 501.

Depending on the etch patterns defined by mask 15, the laterallyinjected hole current component can be adjusted. The etch patterns canbe one dimensional, or two dimensional. A simple one dimensional patternis a group of parallel strips, and a simple two dimensional pattern canbe formed by two groups of parallel strips intercrossing from eachother. Shown in FIG. 6 is an example of the so-formed two dimensionalpattern, a square grid formed by two perpendicular groups of parallelstrips. Referring FIGS. 2B and 6, when FIG. 6 is taken as a top view ofan example structure of FIG. 2B, the upwardly protruding strips areformed by a stack of the remaining p-type layer 40′, the remaininginsulating layer 30′ and, optionally, a certain thickness of n-typelayer 20 (if n-type layer 20 is being partially etched while etchingp-type layer 40 and insulating layer 30) with an upper surface 401. Therecessed squares surrounded by the strips expose the upper surface 201of n-type layer 20 for receiving recovery n-type layer 221 or for directepitaxial growth of active-region 501. The recessed squares may bereplaced by other regular or irregular shapes such as triangle, polygon,circle, or the combination of different shapes.

In this case the laterally injected hole current component isproportional to (2d·a/(a²+2d·a)) (additional resistance from remainingp-type layer 40′ is not considered), here d and a are the strip's (orsidewall's) width and the recessed square's length, respectively. Insome embodiments, strip width d is in the range of 1-10 μm, and squareside length a in the range of 5-50 μm. Since MQW active-region 502 grownon top of the remaining p-type layer 40′ does not contribute tolight-generation, d is not preferred to be too wide. On the other hand,since laterally injected hole current is nearly proportional to d, d hasto be large enough.

Another two dimensional pattern is shown in FIG. 7 with square lattice.FIG. 7 can be taken as a top view of another example structure of FIG.2B. The circles with diameter d represent upwardly protruding lateralhole injecting cylinders, where d is less than a/2, for example lessthan a/4 or a/8, and a is the two dimensional lattice constant. In thiscase, the upwardly protruding lateral hole injecting cylinders areformed by a stack of the remaining p-type layer 40′, the remaininginsulating layer 30′ and, optionally, a certain thickness of n-typelayer 20 (if n-type layer 20 is being partially etched while etchingp-type layer 40 and insulating layer 30) with an upper surface 401. Therecessed areas other than the upwardly protruding lateral hole injectingcylinders expose the upper surface 201 of n-type layer 20 for receivingrecovery n-type layer 221 or for direct epitaxial growth ofactive-region 501. Here, the laterally injected hole current isproportional to (d/a)². The upwardly protruding lateral hole injectingcylinders may have other regular or irregular cross-sectional shapesother than circle shape.

All other suitable one or two dimensional patterns can be used in theseembodiments. Optionally, a thin insulating layer (not shown in FIG. 2Cand FIG. 2D) can be deposited between p-type layer 60 and MQWactive-region 501, for example in direct contact with MQW active-region501, then the perpendicular hole injection into MQW active-region 501 isforbidden and only the lateral injection path is open, realizing acompletely hole lateral injection. If desirable, p-type layer 60 can bemade partially in contact with MQW active-region 501, e.g., the thininsulating layer only covers a portion of MQW active-region 501 and theother portion of MQW active-region 501 is exposed to p-type layer 60. Asexplained in the previous sections, lateral hole injection reduces heatgeneration in an active-region, especially in an MQW active-regionassociated with valence band discontinuity, and results in a moreuniform hole distribution in the active-region.

FIG. 3A-FIG. 3C illustrate a structure and fabrication process flow ofan LED capable of laterally injecting electrons into an active-region,especially an MQW active-region according to another embodiment of thepresent invention. Lateral electron injection has the same importance aslateral hole injection since this will minimize the possibility of hotelectrons and electrons overflow in an MQW active-region. In terms ofreducing heat in MQW active-region, lateral electron injection isexpected to play a more important role since the bandgap discontinuityis mostly distributed in conduction band (accounts for 60-80%). As shownin FIG. 3A, an n-type layer 20 is deposited over a substrate 10. Then-type layer 20 can be grown homoepitaxially or heteroepitaxially onsubstrate 10. In the case of heteroepitaxial growth, n-type layer 20 maycontain other layers used as buffer to accommodate the lattice mismatchbetween n-type layer 20 and substrate 10. In the case of GaN-based LEDs,n-type layer 20 can be made of Si-doped GaN. N-type layer 20 can be anysuitable n-type layer conventionally used in the field. Substrate 10 canbe GaN, sapphire, silicon carbide, gallium arsenide, and the like usedin the field. On top of n-type layer 20 is formed an insulating layer30. It can be insulating GaN such as intrinsic GaN, iron doped GaN, orhighly compensated doped GaN, or insulating AlGaN or AlN. Insulatinglayer 30 is used for electrical isolation so its resistivity ispreferred to be high, preferably to be higher than 100 Ω·cm, morepreferably to be higher than 1000 Ω·cm, and its thickness should begreater than 0.1 μm, preferably be from 0.2 to 0.5 μm.

Mask 15 is used to define desirable one dimensional or two dimensionalor irregular etch patterns such as those discussed previously. Etchdepth should be large enough to allow MQW active-region 501 to bepartially embedded in the recessed area of remaining n-type layer 20′(FIG. 3B and FIG. 3C). Referring to FIG. 3C, the combined etch depth ofinsulating layer 30 and n-type layer 20 is preferably in the range of0.3 to 1.0 μm. MQW active-regions 501 and 502 are then depositedlayer-by-layer simultaneously over the exposed top surface 201 of theremaining n-type layer 20′ and the top surface 301 of the remaininginsulating layer 30′. The MQW active-region 501 is in general made ofalternate AlInGaN quantum barriers and AlInGaN quantum wells, with GaNor InGaN barriers and InGaN wells as a special case. Finally, over MQWactive-regions 501 and 502 a thick p-type layer 60 is grown to finishthe structure. Depending on the etch depth and the regrowth thickness,p-type layer 60 can have a flat surface (FIG. 3C) or an uneven surface(not shown). When the surface of p-type layer 60 is uneven, othermaterials with different refractive index can be filled to smooth theuneven surface of p-type layer 60, such as filling material 70 as shownin FIG. 2D.

When the device is forward biased, hole current and electron current aredriven into MQW active-region 501, illustratively shown respectively byhollow arrows and solid arrows in FIG. 3C. Since the arrangement is thatMQW active-region 501 strides over the sidewalls of the projectionportions of remaining n-type 20′ and the sidewalls of the remaininginsulting layer 30′, leakage current bypassing MQW 501 is forbidden.

In addition, referring to FIG. 3C, recovery layers 221 and 222 can beformed similarly as recovery n-type layer 22 described in connectionwith FIGS. 2A-2D. Furthermore, recovery layers 221 and 222 in thisembodiment can be either an n-type layer or an insulating layer. Whenrecovery layer 221 is an n-type layer, the lateral injected electroncurrent is regulated by the cross-section area ratio of sidewalls of theprojection portions of the remaining n-type layer 20′ and the recessedsurface area of the remaining n-type layer 20′ covered by the recoverylayer 221. When recovery layer 221 is an insulating layer, then theperpendicular electron injection into MQW active-region 501 is forbiddenand only the lateral injection path is open, realizing a completelyelectron lateral injection. When recovery layer 221 is an insulatinglayer, if desirable, the insulating layer 221 can be made only to covera portion of the recessed surface area of the remaining n-type layer20′, allowing partial perpendicular electron injection into MQWactive-region 501.

The remaining insulating layer 30′ serves to insulate the remainingn-type layer 20′ from the p-type layer 60. As long as it can serve thispurpose, the portion of the remaining insulating layer 30′ that imbeddedinto MQW active-region 501 is preferably as thin as possible so that theprojection portions of the remaining n-type layer 20′ can have morecontact area with MQW active-region 501, allowing more lateral electroninjection from remaining n-type layer 20′ into MQW active-region 501.Preferably, more than 50% of the thickness of active-region 501 isembedded into the recesses of remaining n-type layer 20′, for example,more than 60%, 70%, or 80% of the thickness of active-region 501 isembedded into the recesses of remaining n-type layer 20′.

It should be noted that various layers in the embodiment shown in FIG.3A-3C are the same as or similar to the corresponding ones in theembodiment shown in FIGS. 2A-2D, and can be formed in the same orsimilar process as used in the embodiment shown in FIGS. 2A-2D.

The remaining insulating layer 30′ and the corresponding projectionportions of the remaining n-type layer 20′ below the remaininginsulating layer 30′ may have any suitable one or two dimensionalpatterns or any suitable regular/irregular patterns such as those shownin FIGS. 6 and 7, or combination thereof. For example, when FIG. 6 istaken as a top view of an example structure of FIG. 3B, the upwardlyprotruding strips are formed by a stack of the remaining insulatinglayer 30′ and certain thickness of remaining n-type layer 20′ with anupper surface 301. The recessed squares surrounded by the strips exposethe upper surface 201 of the remaining n-type layer 20′ for receivingrecovery n-type layer 221 or for direct epitaxial growth ofactive-region 501. The recessed squares may be replaced by other regularor irregular shapes such as triangle, polygon, circle, or thecombination of different shapes. In this embodiment, the strips have thesame dimension as discussed previously. For example, in someembodiments, strip width d is in the range of 1-10 μm, such as 3 μm, or6 μm, and square side length a in the range of 5-50 μm, such as 10 μm,20 μm, 30 μm, or 40 μm.

FIG. 7 can be taken as a top view of another example structure of FIG.3B. The circles with diameter d represent upwardly protruding lateralelectron injecting cylinders, where d is less than a/2, for example lessthan a/4 or a/8, and a is the two dimensional lattice constant. In thiscase, the upwardly protruding lateral electron injecting cylinders areformed by a stack of the remaining insulating layer 30′ and a certainthickness of remaining n-type layer 20′ with an upper surface 301. Therecessed areas other than the upwardly protruding lateral electroninjecting cylinders expose the upper surface 201 of remaining n-typelayer 20′ for receiving recovery n-type layer 221 or for directepitaxial growth of active-region 501. Here, the laterally injectedelectron current is proportional to (d/a)². The upwardly protrudinglateral electron injecting cylinders may have other regular or irregularcross-sectional shapes other than circle shape.

Still another embodiment is shown in FIG. 4A-FIG. 4D. As shown in FIG.4A, an n-type layer 20 is deposited over a substrate 10. The n-typelayer 20 can be grown homoepitaxially or heteroepitaxially on substrate10. In the case of heteroepitaxial growth, n-type layer 20 may containother layers used as a buffer layer to accommodate the lattice mismatchbetween n-type layer 20 and substrate 10. In the case of GaN-based LEDs,n-type layer 20 can be made of Si-doped GaN. N-type layer 20 can be anysuitable n-type layer conventionally used in the field. Substrate 10 canbe GaN, sapphire, silicon carbide, gallium arsenide, and the like usedin the field. A mask 15 is formed on n-type layer 20 to define etchpatterns. After being etched by a predetermined thickness, a pluralityof recesses having substantially vertical sidewalls are formed on theremaining n-type layer 20′, which lead to the formation of two groups ofvertically displaced surfaces 201 and 202 separated by a distance d₂.Preferably, distance d₂ is in a range of 0.1 to 0.3 μm. Distance d₂ canalso be smaller than 0.1 μm or larger than to 0.3 μm depending on thespecific structure of a light emitting device. Next, an optionalrecovery n-type layer 22 is deposited on the remaining n-type layer 20′,which includes a recovery n-type layer 221 formed on surface 201 and arecovery n-type layer 222 formed on surface 202. Then, an active-regionsuch as an MQW active-region 50 is deposited, which includes an MQWactive-region 501 formed on recovery n-type layer 221 and an MQWactive-region 502 formed on recovery n-type layer 222. A p-layer 60 isdeposited over MQW active-region 501 and MQW active-region 502. Asdepicted in FIG. 4C and FIG. 4D, MQW active-region 501 and MQWactive-region 502 have some vertically overlapping areas, which serve toprevent leakage current path bypassing the MQW active-region 50. Thevertically overlapping area should at least contain one quantum welllayer, preferably 2-6 quantum well layers. MQW active-region 501 and MQWactive-region 502 are vertically displaced, meaning at least some of thequantum well layers do not continue at the interface between MQWactive-region 501 and MQW active-region 502. In other words, the edgesof at least some of the quantum well layers are exposed by the sidewallsof MQW active-regions 501 and 502, so that electrons or holes can belaterally injected into the quantum well layers via the exposed edgesthereof.

In the embodiment shown in FIGS. 4C-4D, the sidewalls of MQWactive-regions 501 and 502 are substantially vertical. However,non-vertical sidewalls, inclined sidewalls, or other shaped sidewalls ofMQW active-regions 501 and 502 can also be adopted in the presentinvention, as long as the edges of at least some of the quantum welllayers are exposed for receiving lateral carrier injection.

In the embodiment shown in FIGS. 4C-4D, p-type layer 60 and n-type layer20′ are shown a single layer, respectively. It should be understood thatp-type layer 60 can include multiple p-type layers with the same ordifferent composition and n-type layer 20′ can include multiple n-typelayers with the same or different composition.

In the embodiment shown in FIGS. 4A-4B, the group of surfaces 201 are ina same plane and each being a flat surface, the group of surfaces 202are in a same plane and each being a flat surface, and the sidewallsbetween surfaces 201 and surfaces 202 are substantially vertical.However, different surfaces 201 can be located in different planes withdifferent height and can be a non-flat surface, different surfaces 202can be located in different planes with different height and can be anon-flat surface, and the sidewalls between surfaces 201 and surfaces202 can be non-vertical, inclined, or other shape. Accordingly, the topsurfaces of MQW active-region 502 can be located in different planeswith different height and can be a non-flat surface, and the bottomsurfaces of MQW active-region 502 can be located in different planeswith different height and can be a non-flat surface; similarly the topsurfaces of MQW active-region 501 can be located in different planeswith different height and can be a non-flat surface, and the bottomsurfaces of MQW active-region 501 can be located in different planeswith different height and can be a non-flat surface. Illustrated in FIG.4E is an example showing that the top surfaces 202, and resultantly, MQW502, sitting on different plane.

This embodiment is capable of laterally injecting electrons and holes.Holes are laterally injected into MQW active-region 502 while electronsare laterally injected into MQW active-region 501. Since MQWactive-region 501 and MQW active-region 502 both contribute to lightemitting, etch pattern is preferably selected to give approximatelyequal area for the elevated and recessed areas. Though any suitable onedimensional or two dimensional patterns can be applied, as an exampletwo dimensional pattern, a chessboard configuration is shown in FIG. 8,which is a top view of an example structure of FIG. 4B. As shown, theupwardly protruding squares have a top surface 202 and length a₂ in therange of 5-50 μm, for example length a₂ being 10 μm, 20 μm, 30 μm, or 40μm. The recessed squares alternately arranged with the upwardlyprotruding squares have a bottom surface 201 and length a₁ in the rangeof 5-50 μm, for example length a₁ being 10 μm, 20 μm, 30 μm, or 40 μm.Top surface 202 and bottom 201 are for receiving recovery n-type layers222 and 221, respectively, or for direct epitaxial growth ofactive-regions 501 and 502, respectively. The upward protruding squaresand the recessed squares may be replaced by other regular or irregularshapes such as triangle, polygon, circle, or the combination ofdifferent shapes, and the upwardly protruding areas can be equal to,larger or smaller than the recessed areas. In the embodiment shown inFIG. 8, the upwardly protruding areas are equal to the recessed areas(a₁=a₂).

FIG. 6 can be taken as a top view of another example structure of FIG.4B, the upwardly protruding strips are formed by the protruding portionsof remaining n-type layer 20′ with a top surface 202. The recessedsquares surrounded by the strips expose surface 201 of remaining n-typelayer 20′. Here, the recessed squares may be replaced by other regularor irregular shapes such as triangle, polygon, circle, or thecombination of different shapes. One major difference between thisembodiment and the structures shown in FIGS. 2A-2D and 3A-3C lies inthat the adjacent active-regions 501 and 502 in this embodiment share avertically overlapping portion, which serves to prevent leakage currentpath bypassing the MQW active-region 50 and contains at least onequantum well layer, preferably 2-6 quantum well layers. In someembodiments, a vertically overlapping portion of adjacent active-regions501 and 502 contains more than 6 quantum well layers.

FIG. 7 can be taken as a top view of still another example structure ofFIG. 4B. The circles with diameter d represent upwardly protrudinglateral electron injecting cylinders, where d is less than a/2, forexample less than a/4, and a is the two dimensional lattice constant. Inthis case, the upwardly protruding lateral electron injecting cylindersare formed by the protruding portion of remaining n-type layer 20′ witha top surface 202. The recessed areas other than the upwardly protrudinglateral electron injecting cylinders expose surface 201 of remainingn-type layer 20′. Surfaces 202 and 201 are for receiving recovery n-typelayers 222 and 221, respectively, or for direct epitaxial growth ofactive-regions 501 and 502, respectively. Here, the laterally injectedelectron current is proportional to (d/a)². The upwardly protrudinglateral electron injecting cylinders may have other regular or irregularcross-sectional shapes other than circle shape.

Further referring FIGS. 4C-4D, the active-region 50 can be described ascontaining a plurality of volume units, each being defined by a topsurface 5001, a bottom surface 5002 and a sidewall 5003. Each volumeunit contains multiple continuous well layers and barrier layers.Adjacent volume units are vertically displaced so that the top surfacesof the adjacent volume units are not in a plane, or the bottom surfacesof the adjacent volume units are not in a plane. The sidewalls of thevolume units are divided into two groups. One group of sidewalls isexposed to the n-type layer for receiving electrons laterally injectedfrom the n-type layer. The other group of sidewalls is exposed to thep-type layer for receiving holes laterally injected from the p-typelayer. In the embodiment shown in FIGS. 4C-4D, active-region 501contains the group of sidewalls that is exposed to the n-type layer,active-region 502 contains the group of sidewalls that is exposed to thep-type layer. Preferably, each of the sidewalls exposes more than onewell layer, more preferably exposes more than half of the total welllayers. The ratio of the contact surface area between the remainingn-type layer 20′ and the sidewalls of active-region 501 to the contactsurface area between the p-type layer 60 and the sidewalls ofactive-region 502 can be adjusted, for example, in the range of 0.5 to2, preferably 0.8 to 1.5, by adjusting the relative size ofactive-regions 501 and 502. In some embodiments, the ratio is about 1.In some other embodiments, the ratio is less than 0.5, or larger than1.5.

Further referring to FIG. 4B and FIGS. 6-8, in the embodiment shown inFIG. 8, each protruding square 202 and each recessed square 201 areadapted to accommodate one volume unit. In the embodiment shown in FIG.6, each recessed square with bottom surface 201 accommodates one volumeunit, while the strips with top surface 202 that surround the recessedsquares accommodate one continuous volume unit conformable to the shapeof the strips. In the embodiment shown in FIG. 7, each of the upwardlyprotruding lateral electron injecting cylinders with a top surface 202accommodates one volume unit, while the recessed areas with surface 201that surround the upwardly protruding lateral electron injectingcylinders accommodate one continuous volume unit.

In the embodiment shown in FIGS. 4C-4D, all of the volume units have thesame number of well layers and barrier layers, and have substantiallythe same height. The top surfaces of the volume units substantially liein two vertically separated planes, respectively. The bottom surfaces ofthe volume units substantially lie in two vertically separated planes,respectively. However, the present invention is not limited to thisstructure. For example, the top surfaces of the volume units may lie inthree or more vertically separated planes, respectively, and the bottomsurfaces of the volume units may lie in three or more verticallyseparated planes, respectively, as shown in FIG. 4E. It is also possiblethat all of the volume units do not have the same number of well layersand barrier layers, and do not have the same height. The sidewalls ofthe volume units can be substantially vertical, or inclined, or of othershape as long as the edges of at least some of the well layers areexposed by the sidewalls for receiving lateral injection of carriers.

In this embodiment, if layers 221 and 222 are insulating layers, MQWactive-region 501 will have completely lateral electron injectioncontributing to light-generation, while MQW active-region 502 willprobably contribute less to light-emitting since MQW 502 is thenelectrically connected between p-layer 60 and n-layer 20′ via MQW 501.

Also, depending on the etch depth and the regrowth thickness, p-typelayer 60 can have a flat surface (FIG. 4C) or an uneven surface (FIG.4D). When p-type layer 60's surface is uneven, other materials withdifferent refractive index can be filled to smooth the uneven surface.As shown in FIG. 4D, uneven surface of p-type layer 60 is smoothened outby filling material 70. Material 70 can be dielectrics like silicondioxide, silicon nitride, or be transparent conducting oxides like ITO.Selection of proper material 70 can enhance the LED's light extractionefficiency.

FIGS. 4C-4D show p-type layer 60 covers the top surfaces of both MQWactive-regions 501 and 502. Optionally, a thin insulating layer (notshown) can be deposited between p-type layer 60 and the top surfaces ofMQW active-region 501 and 502, for example in direct contact with MQWactive-region 501 and 502, then the perpendicular hole injection intoMQW active-region 501 and 502 is forbidden and only lateral holeinjection is allowed. If desirable, p-type layer 60 can be madepartially in contact with MQW active-region 501 and 502, e.g., the thininsulating layer only covers a portion of MQW active-region 501 and 502and the other portion of MQW active-region 501 and 502 is exposed top-type layer 60. If desirable, other layers such as a p-type layer withhigher energy band than p-type layer 60 can be formed between the p-typelayer 60 and the top surfaces of MQW active-region 502 and 501.

Lateral injection of holes and electrons into the same MQW active regionis achieved in yet another embodiment. As shown in FIGS. 5A-5J, ann-type layer 20 is deposited over a substrate 10. The n-type layer 20can be grown homoepitaxially or heteroepitaxially on substrate 10. Inthe case of heteroepitaxial growth, n-type layer 20 may contain otherlayers used as a buffer layer to accommodate the lattice mismatchbetween n-type layer 20 and substrate 10. In the case of GaN-based LEDs,n-type layer 20 can be made of Si-doped GaN. N-type layer 20 can be anysuitable n-type layer conventionally used in the field. Substrate 10 canbe GaN, sapphire, silicon, silicon carbide, quartz, zinc oxide, glassand gallium arsenide, and the like used in the field. An insulatinglayer 30 is deposited on n-type layer 20. A first mask 15 is formed oninsulating layer 30 to define etch patterns. After etching, first mask15 is removed to expose top surface 301 of remaining insulating layer30′ and top surface 201 of a portion of remaining n-type layer 20′. Thetwo groups of surfaces 301 and 201 are vertically displaced as shown inFIG. 5B, for the following LED structure growth, which starts with thedeposition of an optional recovery n-type layer 22 to recover/refreshthe etched surfaces of n-type layer 20 for next MQW active-regiongrowth. The optional recovery n-type layer 22 includes a recovery n-typelayer 221 formed on surfaces 201 of the remaining n-type layer 20′ and arecovery n-type layer 222 formed on surfaces 301 of the remaininginsulating layer 30′. Then an active-region such as an MQW active-region50 is deposited, which includes an MQW active-region 501 formed on therecovery n-type layer 221 and an MQW active-region 502 formed on therecovery n-type layer 222. A second mask 152 is formed covering MQWactive-region 501 and exposing MQW active-region 502. Etching isconducted to partially or completely remove MQW active-region 502deposited on surfaces 301 or layer 222, so that sidewalls of MQWactive-region 501 are exposed (FIG. 5D-FIG. 5E). Second mask 152 isremoved. Then growth of p-type layer 60 is performed (FIG. 5F). FIG. 5Fshows p-type layer 60 covers both the top surfaces and sidewalls of MQWactive-region 501. Optionally, a thin insulating layer (not shown) canbe deposited between p-type layer 60 and the top surfaces of MQWactive-region 501, for example in direct contact with MQW active-region501, then the perpendicular hole injection into MQW active-region 501 isforbidden and only the lateral injection path is open, realizing acompletely hole lateral injection. If desirable, p-type layer 60 can bemade partially in contact with MQW active-region 501, e.g., the thininsulating layer only covers a portion of MQW active-region 501 and theother portion of MQW active-region 501 is exposed to p-type layer 60. Ifdesirable, other layers such as a p-type layer with higher energy bandthan p-type layer 60 can be formed between the p-type layer 60 and thetop surfaces of MQW active-region 501. Optionally, certain thickness ofactive-region 502 can be left unetched and, in the meantime, thesidewalls of active-region 501 are exposed to p-type layer 60.

A third mask 153 is deposited on p-type layer 60 exposing portions thatalign with the areas where the removed MQW active-region 502 used to beand etching is conducted until remaining n-type layer 20′ is exposed andsidewalls of MQW active-region 501 above the exposed remaining n-typelayer 20′ are also exposed (FIG. 5G-FIG. 5H). With third mask 153 inplace, an n-type layer 223 is deposited on the exposed remaining n-typelayer 20′, being in contact with the exposed sidewalls of MQWactive-region 501, and an insulating layer 302 is formed on the n-typelayer 223 to separate n-type layer 223 from p-type layer 60 (FIG. 5I).The uneven areas (if any) can be filled with optical material 70.Finally, third mask 153 and any depositions thereon are removed to getthe final device structure shown in FIG. 5J.

To adjust the ratio of lateral hole and electron injection, the numberof electron injection plugs formed by n-type layer 223 and theinsulating layer 302 and the number of hole injection plugs formed bythe portions of p-type layer 60 formed between sidewalls of MQWactive-region 501 can be adjusted. For example, the ratio of the numberof electron injection plugs to the number of hole injection plugs can bebetween 0.1 to 2, preferably 0.5 to 1. Or the ratio of the contactsurface between electron injection plugs and the sidewalls of MQWactive-region 501 to the contact surface between hole injection plugsand the sidewalls of MQW active-region 501 can be adjusted, for example,in the range of 0.1 to 2, preferably 0.5 to 1.

As schematically shown in FIG. 5J, holes and electrons are be able to belaterally injected into the same areas of MQW active-region 501. Also,if n-type layer 221 is replaced with an insulating layer, a completelateral electron injection is realized. On the other hand, if a thininsulating layer (not shown in FIG. 5F-FIG. 5J) is deposited between thep-type layer 60 and the top surfaces of MQW active-region 501, forexample in direct contact to MQW active-region 501, then theperpendicular hole injection into MQW active-region 501 is forbidden andonly the lateral injection path is open, realizing a completely holelateral injection. With the presence of an insulating layer 221 and athin insulating layer deposited between the p-type layer 60 and topsurfaces of MQW active-region 501, a complete lateral injection ofelectrons and holes into the same MQW active-region 501 is achieved.This will minimize heat generation in the MQW to the greatest extent,and will have the most uniform carrier distribution the MQW. Ifdesirable, other layers such as a p-type layer with higher energy bandthan p-type layer 60 can be formed between the p-type layer 60 and thetop surfaces of MQW active-region 501.

Further, in the above embodiments, the principle of the presentinvention is illustrated with n-type layers being deposited on asubstrate side. It should be understood that the same principle can beapplied to LEDs with p-layers being deposited on a substrate side. Forexample, in FIGS. 4A-4D, the layers 20 (20′) and 22 (221 and 222) can bep-type layers, and layer 60 can be an n-type layer. Because of thevertically displaced MQW configuration, holes and electrons have lateralinjection paths into the MQW.

Referring to FIG. 1, the lateral carrier injection reduces or avoidsheat generation in the MQW associated with heterointerface banddiscontinuity. This is expected to benefit LEDs' internal quantumefficiency. Also, according to the present invention, the lateralcarrier injection means that all quantum well layers or at least some ofthe quantum well layers in the MQW are electrically connected inparallel. In the prior art LEDs, quantum wells in MQW are electricallyconnected in series. Parallel connection means much less resistance thanseries connection, which is preferred in LEDs. In addition, as shown inFIG. 1, in c-plane nitride-based LEDs, polarization fields within theMQW are in the perpendicular direction, and are against carrier'sinjection if carriers are injected perpendicular to the MQW. Accordingto the present invention, lateral carrier injection will result in muchless heat generation since now carriers are not injected against thepolarization fields.

The MQW used in the present invention can emit monochromatic color, orcan be configured to emit multiple color emissions. In order to emitmultiple color emissions, quantum wells in the MQW may have differentbandgap, i.e., different composition. In the prior art LEDs, because ofthe difficulty to have uniform non-equilibrium electron/holedistribution in the MQW growth direction, it is practically verydifficult to realize multiple color LEDs. The present invention usingdisplaced MQW configuration enabling electron/hole lateral injectioninstead of, or in addition to, perpendicular injection, uniform injectedcarriers in the whole MQW active-region is realized, and multiple-colorLEDs can be fabricated. An example of multiple-color LED is an LEDemitting red, green, and blue emissions, mixed to form high-qualitywhite light.

The present displaced active-region design also allows for very thickactive-region adoption for very high power light emitting devices. Inthe prior art, thick active-region, such as MQW with well/barrier pairsmore than 20 is practically difficult to be utilized, because of theincreasing device forward voltage and light self-absorption. Accordingto the present invention, the active-region is displaced. Thisarrangement on one hand greatly reduces light self-absorption by theactive-region, on the other hand, allows for lateral carrier injectioninto the active-region for a uniform carrier distribution in all thequantum wells. The thicker the active-region, the more the exposedsidewall area of the active-region, thus the greater portion of thelaterally injected current is implemented. This enables more uniformcarrier distribution in the active-region and more light-emittingvolumes. The present invention allows for MQW pairs more than 20barrier/well pairs, preferably more than 50 pairs, for example more than100 pairs. For a 100-pair MQW active-region design, the etch depth fordisplacing the recessed and elevated MQW 502 and 501, for example, d₂ inFIG. 4B, preferably is larger than 2 microns.

The present invention also enables quantum wells with very thickbarriers. In the prior art, quantum barrier thickness is limited to beless than 100 nm because of the injected minority carrier diffuselength. According to one aspect of the present invention, electronsupplier layer and hole supplier layer can contact the active-regionfrom lateral side. This means that carriers can be injected into thequantum wells directly, without the need to pass through the quantumbarriers. Thus very thick barriers can be applied in the LED embodimentsaccording to the present invention. The thickness of individual quantumbarrier layer according to the present invention can be in the range of5 to 1000 nm, for example 10-500 nm, 10-300 nm, 100-300 nm, or 100-200nm.

According to the present invention, the thickness of each individualwell layer can be in the range of 1-5 nm. The total thickness of theactive-region can be in the range from 200 nm to 5000 nm, for example,400 nm to 1000 nm, or 500 nm to 900 nm. The MQW active-region cancontain 2-200 pairs of the well layers and the barrier layers, forexample 10-100 pairs, or 20-50 pairs. In some embodiments, at least twoof the well layers emit different wavelength emissions with a peakwavelength difference at least 10 nm, or at least 20 nm, or at least 50nm.

Though the attached figures in the specification shows starting withn-type layers from substrate, it is understood that the principal of thepresent invention can be applied to structures starting from a p-typelayer.

The present invention has been described using exemplary embodiments.However, it is to be understood that the scope of the present inventionis not limited to the disclosed embodiments. On the contrary, it isintended to cover various modifications and similar arrangement orequivalents. The scope of the claims, therefore, should be accorded thebroadest interpretation so as to encompass all such modifications andsimilar arrangements and equivalents.

1-28. (canceled)
 29. A method for manufacturing a light-emitting devicecomprising: providing an n-type layer deposited over a substrate;patterning the n-type layer to form a plurality of recesses defining afirst group of surfaces and a second group of surfaces verticallydisplaced from the first group of surfaces; depositing an active-regionover and conformable to the surface of the n-type layer, so that a firstportion of the active-region is formed on the first group of surfacesand a second portion of the active-region is formed on the second groupof surfaces, wherein the first portion of the active-region isvertically displaced from the second portion of the active-region; anddepositing a p-type layer over and conformable to the active-region, 30.The method for manufacturing a light-emitting device according to claim29, wherein the step of depositing the active-region includesalternately depositing multiple well layers and barrier layers,sidewalls of the first portion of the active-region that are in contactwith the n-type layer expose at least one well layer and sidewalls ofthe second portion of the active-region that are in contact with thep-type layer expose at least one well layer.
 31. The method formanufacturing a light-emitting device according to claim 29, beforedepositing the active-region, further depositing a recovery n-type layeron the n-type layer, which covers the first group of surfaces and thesecond group of surfaces of the n-type layer.
 32. The method formanufacturing a light-emitting device according to claim 29, beforedepositing the active-region, further depositing an insulating layer onthe n-type layer, which covers the first group of surfaces and thesecond group of surfaces of the n-type layer, but does not coversidewalls connecting the first group of surfaces and the second group ofsurfaces.
 33. A method for manufacturing a light-emitting devicecomprising: providing an n-type layer deposited over a substrate;forming an insulating layer on the n-type layer; patterning theinsulating layer to remove exposed portion of the insulating layer and aportion of the n-type layer below the exposed portion of the insulatinglayer, resulting in a first group of surfaces of a remaining insulationlayer and a second group of surfaces of a remaining n-type layervertically displaced with the first group of surfaces; depositing anactive-region, so that a first portion of the active-region is formed onthe first group of surfaces and a second portion of the active-region isformed on the second group of surfaces; removing the first portion ofthe active-region to expose the remaining insulating layer; depositing ap-type layer over the active-region to cover top surface of theactive-region, wherein a portion of the p-type layer fills the spacethat was occupied by the removed first portion of the active-region toform a plurality of hole injection plugs; patterning and etching thep-type layer to remove some of the hole injection plugs and theremaining insulating layer therebeneath until the n-type layer is exposeso as to form a plurality of electron injection plug holes; anddepositing another n-type layer into the plurality of electron injectionholes to form a plurality of electron injection plugs; and depositinganother insulating layer on the plurality of electron injection plugs toinsulate the plurality of electron injection plugs from the p-typelayer.
 34. The method for manufacturing a light-emitting deviceaccording to claim 33, wherein the step of depositing the active-regionincludes alternately depositing multiple well layers and barrier layers,the hole injection plugs are in contact with at least one well layer,and the electron injection plugs are in contact with at least one welllayer.
 35. The method for manufacturing a light-emitting deviceaccording to claim 33, before depositing the active-region, furtherdepositing a recovery n-type layer on the n-type layer, which covers thefirst group of surfaces and the second group of surfaces.
 36. A methodfor manufacturing a light-emitting device comprising: providing a p-typelayer, an insulating layer, and an n-type layer deposited over asubstrate; patterning and etching the p-type layer and the insulatinglayer until the n-type layer is exposed, so as to form a plurality ofprojections containing a remaining portion of the p-type layer and aremaining portion of the insulating layer; depositing an active-regionwith multiple well layers and barrier layers over the substrate so thatthe projections penetrate the active-region and expose the remainingportion of the p-type layer to more than one well layers.
 37. The methodfor manufacturing a light-emitting device according to claim 36, whereinthe step of patterning and etching the p-type layer and the insulatinglayer etches into the n-type layer for a predetermined thickness.